One tablespoon of shortening plus approximately 1/3 of a teaspoon of water should be mixed together to make the equivalent of 1 tablespoon of butter. Shortening used in recipes or cooking without water does not achieve the desired effect. Water must be added in all butter-to-shortening conversions.
For a recipe that calls for 1/4 cup of butter, 1/4 cup of shortening and 1 1/2 teaspoons of water should be mixed together. For 1/2 cup of butter, 1/2 cup of shortening plus 3 teaspoons of water should be mixed. Shortening with water added is typically a good substitution for margarine or butter, except in recipes for no-bake cookies, fudge or candies with melted butter as an ingredient.